The effect of rising temperatures on the increasing human thermal stress in the Syrian coast

Extreme humid heat events have seen rapid increases globally in recent decades, due to climate change. Extreme humid heat, or the combination of high temperature and humidity, poses a more severe threat to human health than does dry heat alone. Though extremes are particularly dangerous, even moderate levels of humid heat can lead to a variety of health and socioeconomic effects. Maximum and minimum daily values for both temperatures and relative air humidity were used during the warm period of each year of the study, which extended for forty years (from 1977 to 2016) for three climatic stations, describing an important part of the coastal region in Syria. In order to estimate the various levels of heat stress and risk to human health, based on three indices: the Wet-bulb global temperature index (WBGT), the Discomfort Index (DI), and the Humidex (HU), and by calculating the daily values of each index during day and night. Box plots and descriptive analysis were used in order to study the statistical characteristics of the values of climatic elements at coastal stations, and in order to study the characteristics of the distribution of days with heat stress or danger to health during the months of the warm period of the year. Trends were also used to determine the direction and value of the change, whereas the significance of the change was estimated using the Mann-Kendall Test. The results of the three indicators during the study period 1977-2016 showed that the number of days that were accompanied by heat stress or a threat to health included a large number of days in the warm period of the year in all studied regions, especially during the months of July and August. The results also showed a significant recurrence of the number of days characterized by acute heat stress since 1998. The years 2012, 2010 and 2016 were characterized by the presence of a large number of days that were accompanied by a risk to health according to the WBGT index, exceeding 100 days in Latakia and Tartous and 70 days in Safita in the year 2012, and 93 days in Latakia and Tartous and 65 days in Safita during the years 2010 and 2016. On the other hand, the results confirmed a clear trend towards a decrease in the number of days that were accompanied by discomfort or mild stress, compared to a sharp and significant increase in the number of days that were accompanied by severe stress or danger to health, especially during the hot period of the year (from the beginning of June until the end of September), with estimates vary depending on the indicator used. The results, according to the WBGT index, showed that there was a sharp and significant increase in the number of days accompanied by a risk to health in all regions, reaching 54 days in Safita, 53 days in Latakia, and 39 days in Tartous. The results of this research are consistent with many global and regional researches on the increase in heat stress, whose negative effects include agricultural production and natural ecosystems, in addition to its clear effects on human activity and health and labor productivity, especially agricultural work in field conditions, which will have serious consequences as temperature continue to increase under recent Climate change.